1. Field of the Invention
The present invention relates to a polyamic acid resin composition, and in particular an additives type polyamic acid resin composition and molar ratio thereof.
2. Description of the Related Art
Polyimide is widely applied in flexible metal foil substrates of assembly industry due to its excellent thermal resistance, electrical properties, size stability, and softness. Moreover, metal foil substrates may be light-weight, thin, short and small-sized, for application in the electronics industry.
Extrusion coating is a fabrication method conventionally used for fabricating flexible metal foil substrates. The extrusion coating process comprises coating polyamic acid resin on a conductive metal foil, drying the resin to remove organic solvents, and then charging the resin at a high temperature (>350° C.) for a predetermined period of time (>1 hour) under nitrogen for cyclization. Because the cyclization consumes much energy and time, a catalyst, such as one disclosed in JP09302225, may be added to the polyamic acid resin to decrease power consumption and process time. In the process, the polyamic acid is firstly synthesized and then the catalyst is added thereto, wherein the polyamic acid resin and the catalyst have a molar ratio of about 1:2. The catalyst having a pKa value of 0 to 8, comprises substituted or non-substituted nitrogen-contained heterocyclic compounds, substituted or non-substituted amino acid compounds, or phenyl compounds or hetero-aromatic compounds having at least hydroxyl groups and a molecular weight of less than 1000. The polyimide is generally applied in alignment films of LCDs. However, for reducing the cyclization temperature to less than 200° C., the catalyst molar ratio must be two times higher than the polyimide precursor (polyamic acid) molar ratio. Thus, mechanical strength and electrical properties of flexible metal foil substrates fabricating therefrom are reduced due to the high additive amount of the catalyst.
JP2008115377 discloses a nitrogen-contained hetero aromatic compound having at least one imine as a catalyst of a heterocyclic compound. The nitrogen-contained hetero aromatic compound may be a single five or six member ring having at least two nitrogen atoms in the ring, or one nitrogen atom in a single six member ring is replaced with another substitute group. A polyimide resin layer comprising the catalyst, has a reduced thermal expansion coefficient of 15 to 20 ppm/K. However, the catalyst molar ratio is still required to be equal to the polyamic acid resin molar ratio for cyclization in 10 minutes. As such, high amounts of the catalyst reduce the electrical properties of the polyimide resin layer, such that products therefrom may not be applied in printed circuit substrates.
Accordingly, a low amount of proper additives is called-for that may simultaneously decrease cyclization temperature and process period of the polyamic acid, while retaining the physical properties of the polyimide product.